Oxidation of ferrous surfaces



No Drawing.

Patented Dec. 19, 1922.

UNITE STATES PATENT OFFICE.

TITO BONDELLI, OF TURIN, AND QUIRINO SESTI'NI, F BERGAMO, ITALY, ASSIGNORS OF ONE-THIRD TO SESTRON (FOREIGN PATENTS) LIMITED, OF LONDON, ENGLAND.

OXIDATION OI FERROUS SURFACES.

Application filed June 30, 1920. Serial No. 393,199.

(GRANTED UNDER THE PROVISIONS OF THE ACT OF MARCH 3, 1921, 41 STAT. L., 1313.)

.Oxidation of Ferrous Surfaces, of which the following is a specification.

This invention relates to the oxidation of ferrous surfaces, that is to say of iron and steel surfaces, and has for its object to pro-- 'vide an improved process for this purpose.

According to this invention the improved process for the oxidation of ferrous surfaces.

consists in immersing the object, the surface of which is to be oxidized, in an alkaline bath having in solution therein metal, such, for example, as lead, which behaves electro negatively towards iron, so as to produce oxidation of the iron or steel surface, with separation of the metal of the oxide, without use of an electric current. Preferably, the concentration of the alkali is such that the solution boils at about 120130 and preferably also the process is carried out at a substantially elevated temperature. The addition of alkali cyanides or oxidizing agents, such as nitrates, to the bath, for example, 10-20 grams of potassium cyanide, is sometimes advantageous. The surface to be treated must be properly cleaned and polished so that it is brou ht into intimate contact with the bath. The process is particularly applicable to well-finished and smooth parts.

In carrying the invention into effect in one way, a bath is prepared by dissolving by aid of agitation 20 grams of litharge in a solu tion of caustic soda boiling at about 120 C. The object whose surface is to be oxidized is immersed, in the solution which is maintained at a temperature of 120130 C. The optimum temperature at which to remove the object depends to some extent upon the composition of its surface. For example, the heating may be continued until the temperature of the bath rises to 135'140 C.

After a shorter or longer period, depending posit of metallic-lead. When this deposit ceases to increase, the maximum degree of oxidation has been reached. The progress of the operation may be followed by taking the object out of the bath from time to time and lightlyrubbingthe. surface in a vessel of water in order to expose the oxidizedv metal by removing the coat of finely divided lead. When the process is complete, the surface is oxidized a black colour which on perfectly polished surfaces attains .an exceptional depth and intensity and remains unaltered.

The reduced lead is recovered from the bottom of the bath andfrom the washing vessel and may be reconverted into oxide and used again.

The concentration of the lead in the bath may vary Within certain limits. For example, 20-30 grams of litharge per litre may be employed, but for a number of purposes it will be found that a considerably lower concentration, for instance 5-10 grams per litre, is suitable. H

The vessels in which the processis carried out may be of porcelain or of iron with a copper or lead lining.

In our copending application Serial N o.

393,198 a process is described for coloring I a metallic surface, according to which the surface is submitted to anodic oxidation in .an alkallne bath containlng copper in soimmersion of the surface in a concentrated alkaline bath having combined in solution therein a metal which behaves electronegatively towards iron.

3. The process for oxidizing a bright ferrous surface, which consists in simple immersion of the surface in a hot concentrated alkaline bath having combined in solution therein a metal: which behaves electronegatively towards iron.

4. The process for oxidizing a bright ferrous surface, which consists in simple immersion of the surface in an alkaline bath having lead combined in solution therein.

5. The process for oxidizing a bright ferrous surface, which consists in simple immersion of the surface in a hot alkaline bath having lead combined in solution therein.

6. The process for oxidizing a bright ferrous surface, which consists in simple immersion of the surface in a-hot concentrated alkaline bath having lead combined in solution therein.

7. The process for oxidizing a bright ferrous surface, which consists in simple immersion of the surface in a solution of caustic soda at 120-14:0 C. having litharge combined in solution therein.

In testimony whereof we have signed our 20 names to this specification in the presence of two subscribing witnesses.

TITO RONDELLI. QUIRINO SESTINI. Witnesses to the signature of Tito Rondelli:

J. PHILLIPS CRAWLEY, J. W. PATCHING. Witnesses to the signature of Quirino Sestini:

J OUTE JoUmLLY, ANsELMER VILLER. 

